1. Field of the Invention
The present invention relates to a system to detect abnormal cable connections in communication apparatuses, and more particularly to an apparatus to detect any such abnormality as a faulty connection of cables or a cable disconnection in such an apparatus as a carrier terminal apparatus, a repeater apparatus or a node station apparatus for an ATM transfer network.
2. Description of the Prior Art
When line trouble occurs between a pair of mutually opposite communication apparatuses or in a communication system involving a plurality of repeater apparatuses arranged in cascade, the point of trouble occurrence is located by various methods. If the trouble is on a submarine relay line or a long-distance relay line, signals of a prescribed bit pattern are sent from the transmit terminal station, and their reflected wave is detected to measure the distance from the terminal station to the trouble spot and thereby to locate the trouble. Similarly, signals of said bit pattern from the transmit terminal station are detected by each repeater station to detect any trouble in any other repeater station on the way or on the line between repeater stations.
If any repeater station or repeater apparatus is identified as a trouble spot by the above described method, many constituent units of the repeater apparatus or the like (usually in packages, each consisting of a printed circuit board mounting many electronic parts) are tested in a prescribed procedure, and the constituent unit involving the part which caused the trouble is replaced with a new one to restore the line.
Trouble-shooting techniques for repeater apparatuses or the like on a unit-by-unit basis have made significant progress, and many testing apparatuses for that purpose are commercially available, but there remains an area in which no matching progress has been achieved as yet. It is the detection of connection trouble with a multicore cable or a connector between various functional units, i.e. the detection of trouble due to a cable disconnection or the faulty contact of a connector.
Usually, such a repeater apparatus or the like consists of a rack divided into a plurality of subracks and a plurality of functional units plugged into each of these subracks. Each such functional unit (hereinafter referred to simply as "unit") involves one or more packages, each consisting of a printed circuit board mounting LSIs and other parts. To the back face of each subrack is fixed a wiring back board, and on the surface of the board is printed the wiring between the many packages to be plugged into the subrack.
Whereas the connection among the units (or packages) to be accommodated by a subrack is thus formed by a wiring back board, that among units on two or more subracks (inter-subrack unit-to-unit connection) has to rely on a multicore cable or cables. Moreover, since the large number of units in such a repeater apparatus or the like are hierarchically grouped from the lower to the upper level because of the nature of transmitted signals, which are frequency-division or time-division multiplexed, and subracks are assigned according to the level in the hierarchy, the number of inter-subrack unit-to-unit connections tends to become great, and so does that of multicore cables accordingly.
At least one end (usually both ends) of each of these many multicore cables is connected by a connector. Therefore, not only the quality of each of these multicore cables and that of the cable-to-connector connection but also the state in which the connector is mounted affects the operation of the apparatus. In spite of the risk these constituent parts entail, no repeater apparatus or the like according to the prior art is provided with means to detect connection trouble with said multicore cables and connectors forming inter-subrack unit-to-unit connections. As a consequence, once any line trouble due to a faulty connection of said multicore cable and connector occurs, it takes a long time to restore normal line connection.